Although there are numerous kinds of bicycle shock absorber devices, most can be classed into the two main categories as transmission system-related and non-transmission system related. Of these, the so-called non-transmission system related variety mainly consists of systems installed on the front end of a bicycle frame, such as on the front fork, handle bar, stem and seat post, which are directly installed and have an integrated resilient component (such as a coil spring, leaf spring or elastomer, etc.). Since this type of installation is does not directly connected to the transmission system, they are simpler and less complex and of course the shock absorption characteristics are mainly focused on the hands of the rider and provide no benefits to the body of the rider. Furthermore, the so-called transmission system-related variety mainly consists of rear stays (such as the seat stays and chain stays in which the rear wheel is mounted) that are not fixed, but active installations equipped with a shock absorber that provides effective shock absorption characteristics for the body of the bicycle rider. In terms of shock absorption performance, the aforesaid variety is further divided into the three categories of low pivot point shock absorption systems, high pivot point shock absorption systems and linked axle-type shock absorption systems, with each category having several dozen variations of respective shock absorption devices. The aforesaid low pivot point shock absorption system refers to a pivot point at the rear wheel that is resilient in upward and downward movement and is positioned below the center line of the front and rear wheels. As indicated in FIG. 1, the shock absorber (30) is installed in between the seat stays (11) and the top tube (13), and the chain stays (12), in addition to having one end conjoined to the lower end of the seat stays (11), the other end is below the center line (C) of the front wheel (A) and the rear wheel (B), with the active installation near the bottom bracket (14), which enables, when the rear wheel (B) subjected to impact, the providing of a resilient upward and downward movement of the pivot point (M) to achieve effective shock absorption. This type of structure can be said to be structurally simpler, lighter in weight and results in reduced chain stretch during shock absorption operation, and although having the advantage of less effect on the transmission system, when the rear wheel is subjected to impact, the locus of wheel movement tends to be upward and forward, which produces a loss of wheel traction. Furthermore, the bicycle frame flexes when large physical objects are encountered. Since the aforesaid structure provides for rear wheel mounting at the seat stays and chain stays, and is not a solidly anchored active installation, whether riding or during brake application, wobbling readily occurs in the aforesaid rear wheel (wheel wobble increases in direct proportion to the assembly clearances of the seat stays and chain stays), and during braking operation, the braking force increases the shock absorber pressure, which decreases shock absorption efficiency and affects structural integrity. In the high pivot point shock absorption system, as indicated in FIG. 2, the middle of the high pivot point (M) is above the center horizontal line (C) of the rear wheel (B). With this type of structure, since the pivot point is positioned over the center horizontal line of the rear wheel, therefore, after shock absorption, the rear wheel moves rearward and is capable of automatically producing a horizontal shock absorption effect. As a result, when the rear wheel is impacted, reduction in bicycle speed is minimal and the bicycle rider feels less impact. However, the chain stretch tension increases considerably and pedal rebound force becomes greater, which produces adverse effects on the transmission system, and the aforesaid pedal rebound force is directly transferred to the bicycle rider, with the shortcoming of creating discomfort to the bicycle rider. Naturally, since the seat stays (11) and the chain stays (12) are both active installations, therefore, the aforementioned wobble produced by the rear wheel as well as the increased shock absorber (30) pressure from the application of bicycle braking force cannot be improved upon. Furthermore, the linked axle-type shock absorption system, as indicated in FIG. 3, is a high pivot point design with the pivot point (M) located above the center horizontal line (C) of the rear wheel (B). However, the aforesaid bottom bracket (14) is designed to move together with the rear wheel (B) and since the aforesaid bottom bracket moves with the rear wheel, therefore, during shock absorption, the advantages are that the effect on the transmission system is lessened and there is no pedal rebound. However, due to the simultaneous movement design of the bottom bracket and the rear wheel, the bicycle rider enjoys the shock absorption performance when riding in a seated position, but all shocks due to ground surface irregularities are transmitted to the rider when riding in the standing position, thereby resulting in periods when all shock absorption characteristics are predictably absent. Furthermore, during shock absorption operation while riding in the standing position, the feet are continuously subjected to shock from the ground surface, which adversely affects the comfort of the rider. Naturally, since the seat stays and the chain stays (12) are active installations, therefore, wobbling occurs in the aforesaid rear wheel and the force of brake application increases shock absorber (30) pressure, both of which cannot be overcome. In other words, although the three shock absorption systems consisting of the aforesaid low pivot point, high pivot point and linked axle-type each have the advantage of being usable, each type has several shortcomings. To the user, this obviously presents certain advantages and inconveniences in application. Furthermore, during the shock absorption operation of each type, the aforesaid rear wheel moves upward and downward and, therefore, conventional baggage racks that are mounted over the rear wheel cannot be installed or cushioned by the shock absorption structure.
Of course, in the meanwhile manufacturers have provided resilient component shock absorbers installed at the seat post of saddles such that during shock absorption, the aforesaid rear wheel cannot move upward and downward, thereby improving upon the shortcomings of the aforesaid transmission system effects as well as the inability to install baggage racks. However, the structure is still completely ineffective when riding in the standing position and, furthermore, although the saddle moves upward and downward while riding in the seated position, the pedals are incapable of a matching upward and downward movement, of which the resulting shortcoming is discomfort to the feet of the bicycle rider.
In summation, the foregoing description conveys the knowledge that the aforementioned structure of the conventional bicycle shock absorption devices obviously still have a number of utilization shortcomings that can be improved.